## Core Concept
The management of thyrotoxicosis during pregnancy requires careful consideration of both the mother's and the fetus's health. The condition can lead to significant complications if not properly managed. The drug of choice should effectively control hyperthyroidism while minimizing risks to the fetus.

## Why the Correct Answer is Right
Propylthiouracil (PTU) is often considered the drug of choice for treating hyperthyroidism in the first trimester of pregnancy due to its lower risk of teratogenicity compared to methimazole. It works by inhibiting the synthesis of thyroid hormones. PTU is particularly preferred during the first trimester because it has a lower risk of causing congenital anomalies compared to methimazole.

## Why Each Wrong Option is Incorrect
* **Option A:** Methimazole is not the preferred choice in the first trimester due to its higher risk of congenital anomalies, such as esophageal atresia and choanal atresia, compared to PTU.
* **Option B:** Radioactive iodine is contraindicated in pregnancy because it can cross the placenta and destroy the fetal thyroid gland, leading to fetal hypothyroidism or even abortion.
* **Option D:** Beta blockers can be used to manage symptoms of hyperthyroidism, such as tachycardia and tremors, but they do not treat the underlying cause and are not sufficient as monotherapy for hyperthyroidism.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the management of thyrotoxicosis in pregnancy often involves switching from PTU to methimazole after the first trimester due to the risk of PTU-induced liver toxicity. This highlights the importance of monitoring liver function tests in patients on PTU.

## Correct Answer: C. Propylthiouracil (PTU).